Cases and covers for mobile phones, tablet computers and other handheld electronic devices may include ornamental decorative elements or visual display features. For example, cell phone cases may include a chamber containing liquid and glitter or sparkling elements that cascade down through the liquid and are visible externally through a transparent cover portion of the case. In previously known products, the hard plastic cover is ultrasonically welded to the hard or soft plastic main back shell on the outside. This exposes the delicate ultrasonic welding joint to outside forces like pressure, drop impact, etc., leading to frequent breakage and leakage of the contents of the sealed liquid filled chamber. Such cases can be prone to leaking of the liquid from the chamber, and needs exist for improved cases and improved methods for manufacturing such cases that reduce the incidence of leaking. It is to the provision of a case or cover for an electronic device meeting these and other needs that the present invention is primarily directed.